Patients suffering from chronic obstructive pulmonary diseases and neuro-muscular diseases often require support ventilation while sleeping in order to prevent the occurrence of carbon dioxide narcosis. This type of ventilation generally requires the installation of a tracheostomy tube. Because the tracheostomy tube remains in place during the day, it is generally desirable to attach a one-way, or speaking valve, to the outward end of the tracheostomy tube. The valve allows the patient to carry on conversations.
Patients complain that the speaking valves are uncomfortable because of the initial effort required to bias the valve open at the beginning of each inhalation. This increased effort can exhaust the patient. Mucus contamination of the valve can significantly increase the effort required to bias the valve open.
The typical speaking valve consists of a flexible disc-shaped diaphragm that collapses inward upon inhalation and seals against a fixed surface upon exhalation. There are two variations of this type valve. In the first variation, of which the description in U.S. Pat. No. 3,137,299 to Tabor is exemplary, the disc-shaped diaphragm is attached to the valve housing through its center. In the second variation, the disc shaped diaphragm is attached to the valve housing along one edge. U.S. Pat. No. 4,040,428 to Clifford is exemplary of this variation.
Valve sticking can become a problem with these types of valves because, as mucus accumulates, the flexible diaphragm can become tacky and begin to adhere to the fixed surface during each exhalation. Since the diaphragm is now adhering to the fixed surface, the patient must expend more force inhaling to create a vacuum in the conduit of the valve housing which is sufficient to free the edge of the diaphragm from the fixed surface. This can become very uncomfortable after even a short period of time. It would be desirable, therefore, to have a tracheostomy valve which would require less inhalation effort to bias open even when the seal becomes tacky.
In addition, the fixed surface which forms part of the sealing mechanism is located adjacent the inner surface of the conduit portion of the typical speaking valve housing. This means that there is a greater likelihood of mucus accumulation on or near the sealing surfaces of the valve. It would be desirable, therefore, to have a tracheostomy valve which would have the sealing surfaces located within the conduit portion of the valve housing at a location away from the inner surface of the conduit, thereby minimizing the accumulation of mucus on the sealing surfaces.
Also, because the typical speaking valve has a fixed surface as a part of its sealing mechanism, only one force acts to separate the surfaces when they begin to adhere. The force acts against the diaphragm and is directly proportional to the pressure differential between the ambient atmosphere and the vacuum created in the valve housing conduit by the expanding lungs, and the surface area of the diaphragm. In order to generate a greater opening force, it is necessary to either increase the surface area of the diaphragm or increase the pressure differential between the ambient atmosphere and the valve housing conduit. Since it is desired to open the valve with the smallest pressure differential possible, it is desirable to have a tracheostomy valve which includes force generating surfaces which have a surface area greater than the cross-sectional area of the valve housing conduit. It would be an additional benefit if a second force were generated which acts conjunction with the first force to open the valve.